Human immunodeficiency virus (HIV), the etiologic agent of acquired immunodeficiency syndrome (AIDS) is the fastest growing cause of death in women of reproductive age. Worldwide, the heterosexual transmission of AIDS is the prevalent mode of transmission of AIDS, accounting for about 90% of all HIV infections in women. Therefore, significant attention has been directed to investigating measures that block sexual spreading of HIV infection. As there is no effective treatment or vaccine against AIDS, preventive measures are the primary tools that can presently reduce transmission of HIV. For example, the consistent and correct use of condoms represents an effective barrier to prevent HIV transmission. However, the risk of acquiring infection can only be significantly reduced if condoms are used for almost all sexual intercourse in HIV prevalent communities; a result that can not be achieved despite intensive prevention programs to increase condom use.
Significant emphasis has been placed on the development of intravaginal microbicidal agents capable of preventing and/or reducing the spread of a variety of sexually transmitted diseases (STDs) in addition to Herpes Simplex Virus (HSV) and HIV. The development of microbicides for topical use represents an important alternative to condom usage. A microbicide is any agent that kills or deactivates disease-causing microbes, including viruses. According to the International Association of Physicians in AIDS CARE (IAPAC), the definition of microbicides also includes interventions that can block or prevent infection, as well as amplification of the body's natural defenses to prevent infection through sexual acts.
Ideally, microbicides should have little or no side effects at an effective microbicidal concentration. Accordingly, the drug used as a microbicide should have little or no immunosuppressive activity at an effective microbicidal concentration. In addition, the ideal microbicide should sufficiently withstand varying temperatures and acceptably function within varied pH ranges (ranges of alkaline and acidic levels in the vagina). Further, it should not eliminate the natural beneficial lactobacilli that reside in the vagina and contribute to vaginal health.
Topical microbicides would be even more beneficial if they also had contraceptive capabilities. Contraception is also important for women with STDs to prevent transmitting diseases future generation, especially since many women with STDs are of childbearing age. At present, a majority of commercially available dual-purpose spermicidal microbicides have detergent ingredients that disrupt cell membranes. The most widely used vaginal spermicide, nonoxynol-9 (N-9), because of its membrane disruptive properties, has been shown to damage the cervicovaginal epithelium, cause an acute inflammatory tissue response, alter vaginal microflora, and enhance the risk of promoting opportunistic infections in the genitourinary tract. N-9 is also toxic to vaginal and cervical cells which increases the permeability of vaginal tissue. It can also kill the Lactobacillus sp. that populate the vaginal tract and are generally regarded as beneficial. Lactobacillus produce lactic acid and hydrogen peroxide, which helps maintain the acidic pH of the vagina (˜pH 3.5 to 5.0) and a healthy vaginal flora. At this pH, a number of STD-causing organisms like HIV are inactivated.
Other spermicidal microbicides in the form of vaginal creams and ointments are currently available over the counter or by prescription. Still others are in various stages of development. Examples include octoxyno1-9 and benzalkonium chloride. Gels designed to control vaginal pH are also available, such as AciJel™ (Ortho-McNeil Pharmaceutical Corp., Raritan, N.J.) which is a water dispersible buffered gel having a pH of 3.9 to 4.1. It is used to restore and maintain normal vaginal acidity. Such gels are designed to control vaginal pH and are not specifically designed to prevent STDs and/or contraception, and thus do not always possess effective microbicidal activity.
As discussed, presently marketed vaginal contraceptive compositions, often containing N-9 as an active ingredient, are generally known in the art. While presently marketed vaginal contraceptive formulations aid in preventing pregnancy, their ability to effectively prevent STDs, particularly HIV/AIDS, is very limited. Moreover, recent analyses show that N-9, when used frequently by women at high risk may actually increase the risk of HIV infection (WHO 2002, WHO/CONRAD technical consultation on nonoxynol-9, Geneva).
Additionally, several microbicides under development contain anti-retroviral agents that had originally been developed for the treatment of patients with HIV infection. However, only temporary and limited benefits are observed in HIV-infected patients treated with any of the actual anti-retrovirals or combinations thereof. The limited ability of these agents to decrease viral burden, the rapid development of resistance and the toxic side-effects of most drugs has limited their long-term efficacy. One major problem associated with the administration of antiviral agents to patients is their poor ability to penetrate and target infected cells. Rapid drug clearance and the toxicity of parent compounds or metabolites also constitute some of the major drawbacks that may slow down the development and use of many antiviral agents. Given the severe toxicity of antiviral agents actually available to treat AIDS and other viral diseases and their limited ability to target infected cells, strategies aimed at reaching therapeutic levels of drugs into infected cells and reducing toxicity is needed.
One of the more recently studied antimicrobials is BufferGel™ (ReProtect LLC, Baltimore, Md.), which has undergone clinical trials. It is a negatively charged, non-absorbable, high molecular weight polymer gel that is designed to maintain vaginal pH below 5 in the presence of semen. As detailed in U.S. Pat. No. 5,617,877, BufferGel™ formulated from a polymer comprised of carboxylated monomers. The polymers have buffering capacity which help control the vaginal pH. However, for contraceptive purposes, BufferGel™ is designed to be used with a device to be inserted into the vagina and positioned over the cervix. As such, to be effective, the device must remain in position over the cervix. Removal of the device or a shift of its position relative to the cervix can destroy, or at least significantly reduce, its effectiveness.
Recent studies have shown that a significant contribution to the antimicrobial properties naturally present in the vagina is primarily due to the microbicidal activity of the lactic acid molecule, and is not necessarily due to low pH alone or to the presence of hydrogen peroxide. (O'Hanlon et al., BMC Infect Dis., 11:200, 2011). In particular, it has been shown that in vaginal fluid, bacteria associated with bacterial vaginosis can be suppressed with lactic acid, but to a much lesser extent with other acids at the same pH.
Accordingly, there is a need for dual purpose contraceptive microbicide and antiviral compositions and methods that provide improved contraceptive and microbicidal activity in order to prevent or reduce the risk of transmission of STDs, including HIV and HSV-2 while simultaneously preventing unwanted pregnancies. Such compositions should be useful for vaginal administration in effective doses that do not inactivate Lactobacillus sp. or cause overt vaginal irritation or other toxicity.